Thanks guys.
Yes the prices are out there.
The damn thing has 4 of them.
GTC, the popping was channel specific and swapping them around moved the popping but it occasionally lets out a pop from one or both channels.

Yes the 6GW8 has become an audiophool valve!

With a small wiring change you can substitute a 6GV8 (in pairs for your set) - you will find these are MUCH cheaper. They were designed as a TV vertical deflection valve but they are very similar to the 6GW8, albeit with different pin connections.

Kriesler actually used the 6GV8 for audio in the 11-99.

I just looked them up on Tube Depot:

6GW8 / ECL86 $US 59.95

6GV8 / ECL85 $US 4.95

Worth swapping a few wires around??

You may need to increase the bias a little....

Hmm sounds like a good idea. GTC suggested solder joins too. The valves get very hot so I suppose the solder joins on the pins could be suspect. Swapping over to 6GV8 could be a better option so long as it doesn’t compromise the sound or requires component changes etc. I’d need to know what to change

The valves get very hot

Power tubes do get hot because, like rectifiers, they work hard, however, they should not run 'red in the face' -- which would indicate that they are being driven too hard.

That aren’t running red which is good
I’m just thinking about your suggestion regarding solder joins - they all look ok though that doesn’t always mean they are good

I think the 11/97 uses a single cathode bias resistor in each channel. The two output stage cathodes are joined and connected to ground via that resistor, with a capacitor in parallel.

The trick would be, measure the cathode current through that resistor with the 6GW8s still in place. It will be about 50mA.

After making the wiring change and fitting the 6GV8s, measure it again. If it's higher, increase the value of that resistor until you get about the same current. If you still get the same current as with the 6GW8s, leave it as it is.

Both the 6GW8 and the 6GV8 run very hot. That's normal. A plate that glows red hot - not normal!

Thanks Ian
I would still prefer to leave it as original especially if someone after me has to service it. I’ve had my share of working on modified chassis’s and as I’m sure you know, it can be a nightmare trying to sort them out. But if all else fails, changing them to 6GV8s would be good solution

I would still prefer to leave it as original especially if someone after me has to service it.

If you do modify it, best to leave a note inside the cabinet explaining what was done and when.

€�If you do modify it, best to leave a note indie the cabinet explaining what was done and when.”

Most definitely - pity the person who modified the Philco I’ve been working on didn’t offer the same courtesy.

A minor mod. But leave a note in a plastic pocket in the cabinet and you have done your duty.

6GW8s are no longer made and the bottom of the barrel is near. You run the risk with NOS ones of ending up with factory rejects anyway. Or used ones. And at the time, the UK made, Trigon branded 6GW8s were rubbish.

6GV8s are running low too. The last ones I bought from Tube Depot were Canadian Rogers tubes and were quite good.

You need a copy of the circuit with the new pin numbers noted. If you email me a copy of the circuit I could do this for you.

I'll also calculate what the correct bias resistor should be.

Scotty, I got bored stuck at home this afternoon so I worked out the 6GV8 change for your 11-97.

I emailed it to you as a png.

Basically you need to move 6 wires on each socket to their adjacent pins and change the bias resistor from 180 ohms to 270 ohms because the 6GV8 pentode has a slightly lower transconductance than the 6GW8.

Kriesler 11-7 6GW8 to 6GV8

I have some nice photo's of a Thorn radiogram transformer after the chain reaction when one went short. Loosing plate volts on a Pentode can be catastrophic. The screen becomes the plate, can't handle the current & is often destroyed. or seriously compromised.

Document uploaded to Post 26.